Where Have All The Sine Where Have All The Sine Waves Gone?Waves Gone?

David WaittKate Disney

2008 April

Digitizing An Analog World

Digital Television (DTV)Digital Television (DTV)

Starting on 17 February 2009Starting on 17 February 2009 New type of broadcasting that will allow better New type of broadcasting that will allow better

quality picture and soundquality picture and sound More efficient use of the radio spectrumMore efficient use of the radio spectrum The same radio spectrum can now be used for The same radio spectrum can now be used for

other applicationsother applications• Public Safety (Police, Fire)Public Safety (Police, Fire)• Wireless dataWireless data• Other communicationsOther communications• GPS enhancementsGPS enhancements

Digital TelevisionDigital Television

What do I need to do if I use a TV What do I need to do if I use a TV antenna and have an older television?antenna and have an older television?• Need a “converter box” to convert the Need a “converter box” to convert the

received digital signal into analog video and received digital signal into analog video and soundsound

Converter Box

101101000101001001000100111110101001

0100100100100

Nothing is required if Nothing is required if your television already your television already has a Digital TV Tunerhas a Digital TV Tuner

Digital TelevisionDigital Television Different levels of quality Standard Definition TV (SDTV) - SDTV is the basic

level of quality display and resolution for both analog and digital. Transmission of SDTV may be in either the traditional (4:3) or widescreen (16:9) format.

Enhanced Definition TV (EDTV) - EDTV is a step up from Analog Television. EDTV comes in 480p widescreen (16:9) or traditional (4:3) format and provides better picture quality than SDTV, but not as high as HDTV.

High Definition TV (HDTV) - HDTV in widescreen format (16:9) provides the highest resolution and picture quality of all digital broadcast formats. Combined with digitally enhanced sound technology, HDTV sets new standards for sound and picture quality in television. (Note: HDTV and digital TV are not the same thing — HDTV is one format of digital TV.)

DTV...More InfoDTV...More Info

www.dtv.gov

The National Telecommunications and Information Administration (NTIA) is administering the coupon program. For more information, visit the NTIA website at www.dtv2009.gov

Is “Going Digital” Enough?Is “Going Digital” Enough?

Simply digitizing information (Music, Simply digitizing information (Music, video, voice, pictures) for transmission is video, voice, pictures) for transmission is not enough to use the RF spectrum not enough to use the RF spectrum efficientlyefficiently

The information must be transmitted as The information must be transmitted as efficiently as possibleefficiently as possible

Common Wireless Devices TodayCommon Wireless Devices Today

Cell phoneCell phone• GSM GSM

• (850, 900, 1800, 1900 MHz)(850, 900, 1800, 1900 MHz)

• CDMA CDMA • (900, 1900 MHz)(900, 1900 MHz)

Wireless (WiFi, 802.11) Wireless (WiFi, 802.11) (2400, 5100, 5800 MHz)(2400, 5100, 5800 MHz)

Bluetooth Bluetooth (2400 MHz)(2400 MHz)

-> How do these devices use the RF -> How do these devices use the RF spectrum efficiently?spectrum efficiently?

Getting From Here To ThereGetting From Here To There

Cell Site

Ocean

Call routed tosatellite facility or

Optical Fiber

"CentralOffice" ,SwitchFacility

The “Cell” siteThe “Cell” site

Cells are actually “Covered” by multiple cell sites. The cell sites operate on different frequencies so they do not interfere with each other within a given cell.

GSM – GSM – GGlobal lobal SSystem for ystem for MMobile obile communications communications

Time Division Time Division MultiplexingMultiplexing

Cell site Cell site communicates with up communicates with up to 8 phones on a to 8 phones on a single frequency for a single frequency for a short amount of time, short amount of time, “Time Slot”“Time Slot”

Each slot is .004615 Each slot is .004615 SecondsSeconds

AT&T (Cingular), T-AT&T (Cingular), T-MobileMobile

slot 1 slot 8slot 7slot 6slot 5slot 4slot 3slot 2

TIME

CDMA – CDMA – CCode ode DDivision ivision MMultiple ultiple AAccessccess

Phones are assigned Phones are assigned codes that are codes that are embedded into the embedded into the signalsignal

The cell site can The cell site can distinguish between the distinguish between the different codesdifferent codes

The number of phones The number of phones communicating on a communicating on a given frequency is given frequency is determined by the “Bit determined by the “Bit Error Rate”Error Rate”

Verizon, SprintVerizon, Sprint

Code 1 Code NCode 6Code 4Code 3Code 2

Communication with many phonesoccurs on ONE frequency all the time

IEEE 802.11 A/B/G (WiFi)IEEE 802.11 A/B/G (WiFi)

Typical wireless home Typical wireless home routerrouter

Several methods for Several methods for varying the radio varying the radio signal (modulation)signal (modulation)

BPSK, QPSK, QAM 8-16-BPSK, QPSK, QAM 8-16-32-64-128-256 32-64-128-256

QPSK Quadrature Phase Shift QPSK Quadrature Phase Shift KeyingKeying

Vary the phase of Vary the phase of the radio signal to the radio signal to indicate one of four indicate one of four locations (0, 90, locations (0, 90, 180, 270 degrees)180, 270 degrees)

Each “star” can Each “star” can represent 2 bits.represent 2 bits.

Amplitude is Amplitude is constantconstant

180O 0O180O90O 90O

01 11 10 01 00

00

01

10

11

Higher Order ModulationsHigher Order Modulations

8 PSK8 PSK 16 QAM (Quadrature 16 QAM (Quadrature

Amplitude Keying)Amplitude Keying)• The more stars in the The more stars in the

constellation, the closer constellation, the closer they will get to each they will get to each other, and they will be other, and they will be more susceptible to more susceptible to interference, 256 QAM interference, 256 QAM for very short for very short communications linkscommunications links

000

111

110101

100

011

010 001

00001000

1101

11110000

00001011

11001010

1001

0111

01010100 0010

0011

0001

BluetoothBluetooth

Most common Most common use is Bluetooth use is Bluetooth headsets for use headsets for use with cellular with cellular phonesphones

Frequency Frequency Hopping Spread Hopping Spread SpectrumSpectrum

Frequency HoppingFrequency Hopping 79 hopping channels79 hopping channels Used in a random orderUsed in a random order 0.000625 seconds per frequency0.000625 seconds per frequency

TIME, (Time Slots)

Frequency 1

Frequency 8

Frequency 7

Frequency 6

Frequency 5

Frequency 4

Frequency 3

Frequency 2

Why Frequency Hopping?Why Frequency Hopping?

If a few packets of data is lost due to If a few packets of data is lost due to interference, only a very small portion of interference, only a very small portion of the information is lost!the information is lost!

TIME, (Time Slots)

Frequency 1

Frequency 8

Frequency 7

Frequency 6

Frequency 5

Frequency 4

Frequency 3

Frequency 2

What Else Can Be DoneWhat Else Can Be Done

What else can be done What else can be done to encourage to encourage “Frequency Re-Use?“Frequency Re-Use?

This drawing shows very poor use of the radio spectrum. if this was a GSM cellular system with, 10 different frequencies, this system could accommodate 80 phones for the state of California

Reducing Coverage AreaReducing Coverage Area

Reducing the coverage area of each cell site increases capacity, but costs more to deploy the network

Pico-CellsPico-Cells Pico-Cells increase Pico-Cells increase

capacity and improve capacity and improve frequency re-usefrequency re-use

Cell site coverage will Cell site coverage will overlap, but on a overlap, but on a different frequency. different frequency. Sites using the same Sites using the same frequency are spaced frequency are spaced further apartfurther apart

Some pico-cells are Some pico-cells are small enough to be small enough to be located in office located in office buildings in closets!buildings in closets!